Muffler having fluid swirling vanes

ABSTRACT

A muffler for an internal combustion engine has a casing forming an expansion chamber therein. An inlet duct is connected to the casing and projects into the expansion chamber and discharges exhaust fluid into the expansion chamber. The casing tapers in an upstream direction to form a pocket for receiving reverse flow of the exhaust gases and to minimize reverse flow from flowing back into the inlet duct in an upstream direction. In the discharge end of the inlet duct are a set of primary vanes and a set of secondary vanes. The vanes are secured to the walls of the duct and extend radially toward the central area of the duct. The vanes are angled in order to deflect the exhaust fluid flow into a swirling movement as it is discharged into the expansion chamber and maintains that swirling movement while passing out of the casing through the outlet duct.

BACKGROUND OF THE INVENTION

The present invention relates generally to mufflers for internal combustion engines of the type commonly used in motor vehicles. More particularly, the present invention relates to such mufflers which provide improved engine combustion efficiency resulting in improved performance and reduced toxic exhaust emissions levels.

Motor vehicles utilizing internal combustion engines continue to be the favored form of transportation to most people in the developed countries of the world. This is in spite of their many disadvantages the more important of which include toxic exhaust emissions and exhaust noise. Although mufflers can substantially reduce or perhaps even eliminate the exhaust noise, it is commonly believed that they do so at the expense of reduced power output and reduced fuel economy.

Designers of exhaust systems have recognized that improving the effectiveness of exhaust gas flow out of the engine can provide improved combustion efficiency and thereby reduced toxic exhaust emissions. There have consequently been many exhaust system designs that have sought to increase the velocity of exhaust gas flow through the exhaust system and thereby scavenge exhaust gases from the combustion chamber and exhaust ports. Some exhaust header system designs position exhaust pipes around the inner circumference of a collector pipe to produce swirling of the exhaust gases from the collector pipe in a vortex flow and thereby enhance exhaust gas flow therefrom. Such systems have been very effective in improving exhaust as well as intake fluid flow and thereby improving combustion. However, such systems require retuning of the engine and replacement of major engine system components and are thus impractical for many motor vehicle owners.

The particular muffler design is also important in that it can substantially affect the combustion efficiency of the engine. Since muffler replacement is easier than exhaust manifold and pipe replacement, automotive engineers have sought improve the muffler design in order to provide improved exhaust flow and thereby improved combustion efficiency. A muffler is also a very important component of motor vehicles because it reduces their exhaust noise making their use in crowded cities more tolerable. Consequently, many mufflers are designed with the dual purpose of both increasing exhaust flow and attenuating exhaust noise.

There are two basic designs of muffler in contemporary use in modern motor vehicles. These designs are the dissipative type and the reactive type. A dissipative muffler absorbs the sound energy as the exhaust fluid passes through the muffler via fibers or other sound deadening material packed therein. Two primary disadvantages of dissipative mufflers are that they lose their effectiveness over time and are expensive to manufacture. Moreover, dissipative mufflers do not produce good low frequency sound attenuation. The reactive type of muffler attenuates the sound energy by reflecting the sound back toward the source. A reactive muffler is inexpensive to manufacture and provides good low frequency sound attenuation but has the disadvantage of producing high backpressure. Variations on these two basic designs have sought to produce desired sound attenuation without substantially or unacceptably increasing the back pressure on the engine since, as is commonly known, excessive muffler induced back pressure will substantially compromise engine combustion efficiency and reduce engine performance.

Exhaust noise is appreciably reduced by friction effects produced by muffler internal structures and noise-wave effects produced by resonance chambers. However, utilization of such structures increases the complexity, cost and size of the exhaust system. But, a large exhaust system is often very undesirable as motor vehicle space may be limited and ground clearance may need to be high especially for sport utility vehicles. Thus, compactness is a very desirable feature in a muffler used in modern motor vehicles. Compactness and concomitantly reduced weight are especially important for high performance vehicles wherein reduced weight can desirably improve acceleration. In attempts to provide both exhaust efficiency and compactness, many mufflers incorporate various internal structures designed to either improve sound attenuation or improve exhaust flow efficiency. An example of a compact, sound attenuating muffler specifically designed for compactness is disclosed in U.S. Pat. No. 4,574,914 to Flugger. The Flugger muffler is especially useful for high performance motor vehicles because it achieves sound attenuation without significant decrease in engine performance. The Flugger muffler is a reactive type which includes partitions as well as convergently and divergently shaped structures which change the direction of exhaust flow. The Flugger muffler is effective in both preserving exhaust flow efficiency and providing sound attenuation. Nevertheless, its size and shape render it unsuitable for some types of motor vehicles.

Some mufflers are specifically designed to reduce back pressure and thereby improve exhaust gas flow as well as intake induction and combustion efficiency. The goal is improved performance and perhaps fuel economy. An example of such a muffler is disclosed in U.S. Pat. No. 6,213,251 to Kesselring. The Kesselring muffler includes restrictor disk holes and a helical passageway therein to enhance the exhaust gas flow therethrough. The specific goal is moderate backpressure at low rpm and little or negative backpressure at high rpm. Such types of mufflers, however, have inordinate complexity.

Many muffler designs incorporate apertures in the exhaust tubes therein in order to gradually expand the gas stream flowing through the muffler. However, such designs are not very effective at this because since the tubes are straight tubes the major portion of the gas stream flows through and out of the tube and only a small portion flows out through the muffling apertures. Nevertheless, such apertured tubes are in common use in mufflers and some mufflers have used such apertures to provide a swirling exhaust gas stream in order to enhance exhaust gas flow through the muffler. An example of such a muffler pipe design is disclosed in U.S. Pat. No. 6,385,9678 to Chen. The Chen pipe has a conical structure to accelerate the gas stream and spiral portions spaced around the conical structure. However, the Chen pipe is only a part of a muffler and many types of muffler casings would not be suitable for such a pipe.

Despite the prevalence of many types of mufflers, what is needed is a muffler that can curtail reverse flow of exhaust gas toward the engine. What is also needed is a muffler that can provide adequate sound attenuation as well as fuel economy. It is also desirable that these features be provided without sacrificing power output.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide a muffler having structural components that impart a swirling motion to the exhaust fluid flowing therethrough.

It is another object of the present invention to provide a muffler which prevents reverse flow of exhaust fluid therein.

It is also an object of the present invention to provide a muffler that reduces back pressure while providing exhaust sound attenuation.

It is also an object of the present invention to provide a muffler having exhaust fluid swirling components that are shaped to provide minimal restriction of fluid flow therethrough.

Exhaust systems generally are compromised by an inherent exhaust flow inefficiency caused by valve overlap of the internal combustion engine. At the end of the exhaust stroke of the engine's piston, the piston starts to move down while the intake valve is opening to allow the air/fuel charge into the combustion chamber. However, the valve overlap design of modern engines has the exhaust valve also open at this crucial time thereby allowing the combustion chamber to draw exhaust gases directly from the exhaust system. This is especially problematic if the exhaust gas velocity is low and exhaust system pressure is high whereupon the exhaust gases will readily flow backward into the combustion chamber rather than out from the exhaust system. Exhaust gases entering the combustion chamber will dilute the intake fluid with unburnable gases and occupy needed combustion chamber space. This can result in reduced power since there is a lower quantity of fresh air/fuel mixture in the combustion chamber than there otherwise would be. Additionally, the presence of the hot exhaust gases in the combustion chamber may raise the temperature of the mixture above the fuel's knock resistance accelerating engine wear and possibly damaging internal engine components. Consequently, it is imperative that an exhaust system have high fluid flow velocity and therefore low pressure in order to prevent or minimize these effects.

As exhaust gas temperature equalizes in the exhaust system, pressure tends to move in a reverse direction i.e., toward the combustion chamber. This normally happens during deceleration and can cause spent exhaust gases to enter the combustion chamber as a result of the valve overlap (also known as positive overlap). As a result of the reduction in the quantity of power producing fresh air/fuel mixture in the combustion chamber, there will be a slight flat spot during re-acceleration and a reduction in fuel economy.

The muffler of the present invention is specifically designed to prevent reverse flow of exhaust gases that typically occurs during deceleration by providing a pocket within the muffler expansion chamber. The pocket in effect traps the exhaust gases thereby precluding their reentry into the inlet duct of the muffler. During engine operation, the hot exhaust gases discharged into the muffler expansion chamber expand to the walls thereof and upon commencement of the reverse flow move into the pocket where their movement is stopped. As a result, the exhaust gases are trapped in the pocket. The exhaust gases thus collect in the expansion chamber instead of moving back into the inlet duct. When reacceleration takes place, the pocket is emptied as the exhaust flow velocity increases producing a pressure drop in the chamber which draws the gases out of the pocket.

Backpressure which is basically resistance to fluid flow is also necessary to avoid or minimize because high backpressure causes the exhaust gases to remain in the exhaust system too long. When the exhaust gases back up in the system there is an increased tendency for the gases to reverse flow. Thus, it is advantageous for an exhaust system to produce very low backpressure or, more preferably, a vacuum within the system to induce scavenging of the exhaust gases and to thereby aid exhaust flow.

The muffler of the present invention is also specifically designed to aid fluid flow through the exhaust system by causing the fluid to swirl as it moves through the system. The swirl reduces the decrease in exhaust gas velocity that would otherwise occur yielding reduced backpressure. Consequently, this improved flow reduces the tendency of the fluid to reverse flow during deceleration. Overall performance and power output are improved as a result.

The muffler of the present invention achieves its goal of swirling the fluid flow by incorporating vanes which are positioned in the exhaust flow stream. More specifically, the vanes are secured to the inside of the inlet duct. The vanes are angled so that they deflect the fluid laterally into a rotational movement. The vanes thus impart a swirling movement to the exhaust fluid discharged into the expansion chamber thereby enhancing fluid flow in the space utilized to prevent flow reversion.

The vanes are specially curved (at their edges) and shaped for maximal efficiency in producing the swirl effect with minimal fluid flow restriction. The vanes are longitudinally longer at the inner surfaces of the walls of the inlet duct than at the central area of the duct. Thus, the peripheral portions of the vanes are larger and therefore provide more deflection than the smaller, more centrally located portions of the vanes. This is desirable because it more efficiently yields the desired swirl. This is because the swirl produced is essentially exhaust gas rotation about a central axis with the more peripheral gas at peripheral areas of the duct (or chamber) rotating more than the gas at more centrally located areas. Consequently, flow deflection at the peripheral portions of the duct is more effective in producing the desired fluid rotation about the central axis of the duct (and chamber). Similarly, near the central area of the housing the vane portions are smaller producing less deflection and concomitantly less fluid flow restriction at the duct area where swirl can less effectively be produced.

The lower or trailing edges of the vanes are also curved to streamline the vanes for reduced fluid flow resistance. The curvature is in a direction of from the periphery to the center of the duct (or chamber). Since the peripheral ends of the primary vanes are longer than the central (or inner) ends, the lower or trailing edge is angled in the direction of fluid flow and the curvature thereof is also curved in this direction.

Additionally, lower end portions and lower medial end portions of the vanes are bent in the direction of the deflection of the fluid flow. The lower end portions and lower medial end portions are thus angled laterally to enhance deflection of the fluid flow. This deflection provided by these lower portions is also very effective in producing swirl because the fluid flow has been previously deflected by upper portions of the primary vanes and has been moving downwardly alongside the vanes until it reaches these lower portions where it is further deflected to add more lateral movement and thereby more rotational movement to the fluid flow.

Also included are secondary vanes for maximal efficiency in producing the swirl effect with minimal fluid flow restriction. The secondary vanes are mounted in the duct and attached to the walls thereof. The secondary vanes are also angled the same as the primary vanes for producing the desired deflection of the fluid flow. But, the secondary vanes are shorter in width and thus extend only a short distance toward the center and into the inner area of the duct so that they are essentially located only in the inner peripheral area of the duct where there is maximal effectiveness in producing the fluid flow rotational movement.

The present invention obviates the need for a central support structure by interconnecting lateral inner ends of the vanes at the central area of the duct. The central area of the duct is thus open, and there is therefore nothing to impede fluid flow through the center of the duct. Thus, the present invention provides improved exhaust fluid flow over prior art comparable structures. Moreover, elimination of a central member does not result in reduction in the efficiency of the structures in producing fluid swirl because the swirl produced is essentially fluid rotation about a central axis i.e., the center of the duct, with the more peripheral fluid at peripheral areas of the passageway rotating more than the fluid at more centrally located areas. The overall fluid movement is thus in the shape of a spiral as it moves through the passageway. Consequently, the swirl cannot typically be effectively accomplished by means of structures located at the center of the duct but can instead be effectively accomplished by means of structures located at more peripheral portions of the duct. Indeed, maximal twisting or turning of the fluid flow is accomplished by means of structures such as the secondary vanes and structure portions such as the larger peripheral portions of the primary vanes both of which are located at the area of the inner perimeter of the duct.

The muffler of the present invention thus provides an exhaust system component that prevents or reduces reverse flow of the exhaust fluid as well as enhancing fluid flow through the exhaust system. The present invention thus eliminates or minimizes hesitation during acceleration thereby improving performance and improves fuel economy by ensuring a fresh air/fuel mixture in the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the muffler of the present invention shown with a portion cut away to illustrate the components thereof.

FIG. 2 is a longitudinal-sectional view of the muffler of the present invention.

FIG. 3 is cross-sectional view of the muffler of the present invention illustrating inner vane components thereof and taken along lines 3-3 of FIG. 2.

FIG. 4 is a schematic drawing of the muffler of the present invention showing the movement of exhaust gas therethrough.

FIG. 5 is a side plan view of a representative primary vane of the muffler of the present invention.

FIG. 6 is a top view of a representative primary vane of the muffler of the present invention.

FIG. 7 is a rear end view of a representative primary vane of the muffler of the present invention showing the angled lower end portion thereof and also showing the fluid flow passing thereagainst and proximal thereto.

FIG. 8 is a side plan view of a representative secondary vane of the muffler of the present invention.

FIG. 9 is a top view of a representative secondary vane of the muffler of the present invention.

FIG. 10 is a rear end view of a representative secondary vane of the muffler of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, the muffler of the present invention is generally designated by the numeral 10. The muffler 10 includes a casing 12. The casing 12 is hollow and includes an inlet port 14 and an outlet port 16 at opposite ends thereof. The casing 12 also includes a main body 18 defining an expansion chamber 20 in the casing 12 and located between the inlet port 14 and outlet port 16. An inlet duct 22 is connected to the inlet port 16 and has an inlet end 24 for connection to an exhaust pipe (not shown) to allow exhaust fluid 26 from an internal combustion engine (not shown) to enter the casing 12. The inlet duct 22 extends through the inlet port 14 and has an outlet (or discharge) end 28 for discharge of the exhaust fluid 26 into the expansion chamber 20 which has a larger cross-sectional area than the inlet duct 22 (and inlet port 14), as is typical for conventional mufflers. The casing 12 also includes an outlet duct 30 connected to the outlet port 16 for allowing emission of exhaust fluid 26 therefrom and out of the chamber 20. The outlet duct 30 and outlet port 16 are preferably larger in cross-sectional area than the inlet port 14 and inlet duct 22 to reduce resistance to fluid flow.

The main body 18 of the casing 12 includes a front portion 32, a front medial portion 34, a medial portion 36, a rear medial portion 38 and a rear portion 40. The front portion 32 and the rear portion 40 are located at opposite longitudinal ends of the casing 12. The front medial portion 34, the medial portion 36 and the rear medial portion 38 are preferably unitary and preferably cylindrical. However, other suitable shapes may also be utilized instead.

The inlet duct 22 extends into the expansion chamber 20 such that the outlet end 28 is located at the medial portion 36 of the expansion chamber 20. The expansion chamber 20 includes a pocket 42 which is located at the inlet port 14 area. The inlet duct 22 includes an outlet end portion 44, and the outlet end portion 36, the front portion 38 and the front medial portion 34 together define the pocket 42. The front portion 32 is convergently tapered toward the inlet port 14 and in an upstream direction relative to the direction of flow of the exhaust fluid 26. Similarly, the rear portion 40 is convergently tapered toward the outlet port 16 and in a downstream direction relative to the direction of flow of the exhaust fluid 26. The front portion 32 and the rear portion 40 are preferably frusto-conical.

During the crucial deceleration phase of engine operation, the exhaust fluid 26 tends to reverse direction and move rearward. But, the fluid 26 tends to move into the pocket 42 rather than into the inlet duct 22 because there is less pressure in the pocket 42 than in the outlet end 28 and because the expansion of the fluid outwardly from the outlet end 28 as it is discharged therefrom tends to promote flow laterally outwardly and thereby rearwardly into the pocket 42. Once the fluid is moving into the pocket 42, the inlet duct 22 and the front medial portion 36 (and to a certain extent the front portion 32) block lateral movement of the fluid such that it becomes trapped in the pocket 42. As a result of the taper of the front portion 38, the pocket 42 has a smaller cross-sectional area at the inlet port 14 than at the front medial portion 34. The smaller cross-sectional area of the inlet port 14 area of the pocket 42 tends to compress fluid entering therein so that the total quantity of fluid in the pocket is thereby maximized. Consequently, there is a maximal quantity of fluid 26 in the pocket 42 concomitantly minimizing the quantity of fluid available to reverse flow into the outlet end 28 of the inlet duct 22. After deceleration is terminated and reacceleration is commenced, the velocity of the stream of fluid 26 flowing out of the outlet end 28 causes a pressure drop in the expansion chamber 20 so that this pressure drop in conjunction with the higher pressure of the fluid in the pocket 42 due to its compression facilitates fluid flow out of the pocket and subsequently out of the muffler 10.

The muffler 10 also incorporates a set of vanes 46 which impart a swirling motion to the exhaust fluid in order to improve the flow of exhaust fluid 26 through the exhaust system. The set of vanes include a plurality of primary vanes 48 which are preferably mounted in the inlet duct 22. The primary vanes 48 are located at the outlet end portion 44 of the inlet duct 22. The primary vanes 48 are preferably securely attached to the inner surfaces 50 of the walls 52 of the inlet duct 22 via welding or other suitable attachment means.

The set of vanes 46 also include a plurality of secondary vanes 54 which are also preferably mounted in the inlet duct 22. The secondary vanes 54 are similarly located at the outlet end portion 44 of the inlet duct and preferably securely attached to the inner surfaces 50 of the walls 52 of the inlet duct 22 via welding or other suitable attachment means. Each of the secondary vanes 54 are situated between the primary vanes 48 such that the vanes 48 and 54 alternate about the circumference of the inner surfaces 50 of the walls 52 of the inlet duct 22. Both the primary vanes 48 and the secondary vanes 54 are in the path of the exhaust fluid 26 flow.

The vanes 48 have top edges 56 that are in misalignment with bottom edges 58 thereof, and vanes 54 have upper edges 60 that are in misalignment with lower edges 62 thereof. This misalignment is with reference to the direction of fluid flow 64 passing through the muffler 10 during the acceleration phase of engine operation (or longitudinally with reference to the casing 12).

The primary vanes 48 are situated so that the bottom edges 58 are flush with the discharge end edge 29 of the inlet duct 22. However, the secondary vanes 54 are medially situated on the walls 52. Thus, the lower edges 62 are not flush with the discharge end edge 29 of the inlet duct 22.

The primary vanes 48 thus are preferably oriented at an angle such that the flat planar outer surfaces 66 thereof face the fluid flow 64. The secondary vanes 54 are similarly oriented at an angle such that the flat planar outer surfaces 68 thereof face the fluid flow 64. The fluid flow 64 impinging on the surfaces 66 and the surfaces 68 thus is deflected laterally. The vanes 48 and 54 are preferably oriented at an angle of twenty-five degrees with reference to the axis 70 of the casing 12. More specifically, the angular orientation of the vanes 48 is with reference to a plane which includes the axis 70 and the top edge 56 of the particular vane 48. This orientation is with reference to a line or plane which connects the top edges 56 and bottom edges 58 of each particular vane 48. Similarly, the angular orientation of the vanes 54 is with reference to a plane which includes the axis 70 and the upper edge 60 of the particular vane 54. Since the axis 70 coincides with the direction of the fluid flow 64, the angular orientation is also relative to the direction of fluid flow 64 entering the casing 12. Furthermore, the vanes 48 and 54 are also oriented at an angle which is laterally clockwise from a vantage point of fluid flow 64 entering the inlet port 14. Thus, this particular orientation of the vanes 48 and 54 deflects the fluid flow 64 laterally thereby essentially turning it and rotating it in a clockwise direction. This clockwise rotational movement of the fluid flow results in a spiral shaped movement of the fluid flow 64 that exits from the outlet end 28.

The primary vanes 48 have main portions 72, inner lower medial end vane portions 74, outer lower medial end vane portions 76, inner lower end vane portions 78 and outer lower end vane portions 80 which are all flat planar. Each of the main portions 72 are angled twelve degrees with reference to the plane of their respective top edges 56 and axis 70. The lower medial end vane portions 74 and 76 are bent along bend lines 82 so that portions 74 and 76 are angled horizontally in a clockwise direction from the vantage point of the fluid flow entering the inlet port 14 with reference to the plane that includes the top edge 56 and the axis 70 (or direction of fluid flow 64 into the inlet port 14). Thus, the lower medial end vane portions 74 and 76 are oriented in the same direction as main portions 72 of vanes 48. However, in addition to being angled twelve degrees with reference to their respective main portions 72, these lower medial end vane portions 74 and 76 are angled in the same direction as the main portions 72, as described in detail hereinabove. Similarly, the lower end vane portions 78 and 80 are bent along bend lines 84 and 86 respectively so that portions 78 and 80 are angled horizontally in a clockwise direction from the vantage point of the fluid flow entering the inlet port 14 with reference to the plane that includes the upper edge 60 and the axis 70 (or direction of fluid flow 64 into the inlet port 14). Thus, as with lower medial end vane portions 74 and 76, the lower end vane portions 78 and 80 are oriented in the same direction as main portions 72 of vanes 48. The lower end vane portions 78 and 80 are angled twelve degrees with reference to their respective lower medial end vane portions 74 as well as angled in the same direction as the main portions 72. Thus, the fluid flow that has been deflected horizontally by the main portions 72 is further deflected horizontally by the lower medial end vane portions 74 and 76 and subsequently by the lower end vane portions 78 and 80. The fluid flow 64 which passes alongside the main portions 72 and thereby diverted from its previously solely longitudinal direction of movement into a horizontal direction acquires a certain degree of directional stability by the support provided by the angled main portions 72. This directional stability of the fluid flow stream can be relatively easily changed by deflection via the lower medial end vane portion 74 and 76 and the lower end vane portions 78 and 80 in the same horizontal direction thereby increasing the degree of rotational movement imparted to the fluid flow 64. The fluid flow 64 exiting the inlet duct 22 thus swirls to a greater degree due to the angled portions 74, 76, 78 and 80 than otherwise. Deflection of the fluid flow 64 successively in three steps is also more effective than simply angling the entire vane 48 at the same angular orientation as the lower end vane portions 78 and 80. The bend line 86 is preferably perpendicular to the directional line of fluid flow 64. The line 84 is preferably angled at a forty-five degree angle in the direction of fluid flow while the bend line 82 is preferably angled at a sixty degree angle in the direction of fluid flow 64.

The vanes 48 are preferably interconnected at front or inner end portions 88 via interconnection members 90. Vanes 48 are thus formed into pairs of vanes 48. Interconnection members 90 are preferably laterally curved while longitudinally straight such that they are semi-cylindrical in shape. The interconnection members 90 are preferably located proximal to or more preferably adjacent to the central area 92. The members 90 are preferably oriented at an angle of twenty-five degrees relative to the plane including the top edge 56 and the axis 70, as with the vanes 48 and 54. Since the interconnection members 90 interconnect the vanes 48 providing structural rigidity thereto, there is no need for a support structure at the center of the inlet duct 22 to attach the vanes 48 to and thereby provide structural support thereto. Consequently, the central area 92 of the inlet duct 22 is open allowing exhaust fluid 26 to pass freely therethrough. Since the center of the inlet duct 22 cannot pragmatically incorporate structures that can effectively provide swirl to the fluid flow, the lack of a central support structure does not reduce the swirl effect provided but instead minimizes fluid flow restriction of the inlet duct 22.

The vanes 48 are preferably longitudinally longer at peripheral areas 94 of the inlet duct 22 than at the central area 92. Thus, the rear end vane portions 96 are longer than the front end vane portions 98. More specifically, the front end vane portions 98 are twenty-five percent of the length of the rear end vane portions 96. Basically, this difference in length reduces the longitudinal length of the vanes 48 at the more central area where the vane 48 is less effective in producing swirl. In addition, front upper edges 99 of the vanes 48 are curved in the direction of fluid flow 64 and bottom edges 58 are also curved in the direction of fluid flow 64. Edges 99 and 58 are curved toward each other into a converging direction so that the vanes 48 are substantially smaller at the central area 92 than at the peripheral area 94. The front upper edges 99 and the top (or leading) edges 56 first meet the fluid flow 64 so the leading edge 56 is straight to provide larger vane 48 area at the peripheral area 94 where the vanes 48 can more effectively provide swirl while the front upper edge 99 is curved downwardly to provide smaller vane 48 surface area at the central area 94 where the vanes cannot relatively provide swirl.

The vanes 54 are preferably rectangular in shape. Vanes 54 are also preferably longitudinally shorter and laterally (or axially with reference to the casing 12) shorter than the vanes 48.

The vanes 48 and 54 are preferably composed of stainless steel. However, other suitable materials may also be used. Similarly, the casing 12 is preferably composed of stainless steel. However, it may also be composed of galvanized steel or other suitable material.

Accordingly, there has been provided, in accordance with the invention, a muffler for preventing reverse flow of exhaust fluid therethrough and for swirling the fluid flow passing therethrough that fully satisfies the objectives set forth above. It is to be understood that all terms used herein are descriptive rather than limiting. Although the invention has been described in conjunction with the specific embodiment set forth above, many alternative embodiments, modification and variations will be apparent to those skilled in the art in light of the disclosure set forth herein. Accordingly, it is intended to include all such alternatives, embodiments, modifications and variations that fall within the spirit and scope of the invention set forth in the claims hereinbelow. 

1. A muffler for an internal combustion engine, comprising: a casing having an inlet port and an outlet port to allow an exhaust fluid stream to pass through said casing, said casing defining an expansion chamber therein; an inlet duct connected to said inlet port and projecting into said chamber; an outlet duct connected to said outlet port, said outlet duct in longitudinal alignment with said inlet duct, said outlet duct completely closed laterally and completely open at longitudinal ends thereof to allow the exhaust fluid stream to freely flow longitudinally therethrough; a set of vanes mounted within said inlet duct, each vane of said set of vanes extending radially from a peripheral area of said inlet duct toward a central area thereof, said central area extending entire longitudinal length of said inlet duct, said central area entirely open to allow the exhaust fluid stream to freely flow longitudinally therethrough, said inlet duct and said outlet duct providing a longitudinally completely open longitudinal path therebetween and therethrough extending straight through entire longitudinal length of said casing for fluid to flow longitudinally straight and unobstructed through said casing.
 2. The device of claim 1 wherein the said inlet duct extends into and terminates at a medial portion of said expansion chamber.
 3. The device of claim 1 wherein said casing is convergently tapered in an upstream direction at said inlet port to partly define a pocket which is convergently tapered in an upstream direction, said pocket also defined by an outlet end of said inlet duct and constricted at said inlet port to trap reverse flowing fluid stream therein and thereby minimize reverse flow of the fluid stream.
 4. The device of claim 1 wherein said set of vanes are angled in order to deflect fluid of a fluid stream passing through said casing and alongside said set of vanes.
 5. The device of claim 1 wherein said set of vanes includes a plurality of primary vanes and a plurality of secondary vanes, said plurality of primary vanes secured at ends thereof to walls of said inlet duct, said plurality of secondary vanes secured at ends thereof to the walls of said inlet duct.
 6. The device of claim 5 wherein each of said set of primary vanes and secondary vanes are oriented with bottom edge and lower edge thereof positioned in misalignment with top edge and upper edge thereof with reference to direction of fluid flow entering said casing through said inlet port and in a direction of the misalignment which is clockwise from a vantage point of fluid flow entering said casing so that each of said plurality of primary vanes and secondary vanes is at an angular orientation in order to impart a clockwise rotational movement to fluid flow passing thereagainst and thereby through said casing.
 7. The device of claim 6 wherein said inlet duct has a discharge end edge, said top edge of all of said set of primary vanes flush with said discharge end edge.
 8. The device of claim 5 wherein said plurality of primary vanes include main portions, lower medial portions and lower end portions which are angled horizontally relative to said main portions and in a clockwise direction from a vantage point of fluid flow entering said casing through said inlet port.
 9. The device of claim 8 wherein each of said main portions are angled twelve degrees with reference to a plane which includes said top edge and the direction of fluid flow passing through said inlet port.
 10. The device of claim 8 wherein each of said plurality of primary vanes have a bend line for said lower medial end portions, said bend line at a sixty degree angle relative to direction of fluid flow through said inlet port.
 11. The device of claim 8 wherein said plurality of primary vanes have a bend line for said lower end portions, said bend line at a forty-five degree angle relative to direction of fluid flow through said inlet port.
 12. The device of claim 11 wherein said lower end portions are angled twelve degrees relative to said lower medial portions in a horizontal direction and in a clockwise direction with reference to fluid flow passing through said inlet port.
 13. The device of claim 5 wherein each of said plurality of primary vanes have an inner end portion and an outer end portion, said inner end portion longitudinally shorter than said outer end portion.
 14. The device of claim 5 wherein said plurality of primary vanes and said plurality of secondary vanes are flat planar.
 15. The device of claim 5 wherein said plurality of primary vanes include a set of pairs of primary vanes, each of said pairs interconnected adjacent the central area of said inlet duct so that said inlet duct is open at the central area for enhancing exhaust fluid flow through said inlet duct.
 16. The device of claim 15 further including a set of interconnecting members for interconnecting said set of pairs of primary vanes at inner lateral end portions, said set of interconnecting members being laterally curved and longitudinally straight.
 17. The device of claim 5 wherein said plurality of secondary vanes are of substantially shorter width than said plurality of primary vanes and of substantially shorter length than said housing and wherein said plurality of secondary vanes are positioned between said plurality of primary vanes.
 18. The device of claim 1 wherein said set of vanes is positioned at a discharge end portion of said inlet duct.
 19. The device of claim 1 wherein said casing, said inlet duct and said outlet duct are cylindrical.
 20. The device of claim 19 wherein said casing has a diameter which is twice that of said inlet duct, and wherein said outlet duct has a diameter which is larger than said that of said inlet duct.
 21. The device of claim 1 wherein said casing is convergently tapered in a downstream direction at the outlet port to facilitate fluid emission out of said casing and through said outlet port, said outlet port having a larger cross-sectional area than said inlet port to facilitate fluid emission out of said casing and through said outlet port. 